U.S. patent application number 15/126674 was filed with the patent office on 2017-03-30 for conductive paste with improved performance in glass strength.
The applicant listed for this patent is Ferro Corporation. Invention is credited to Terry J. Brown, Jeffery Grover, David Klimas, George E. Sakoske.
Application Number | 20170088718 15/126674 |
Document ID | / |
Family ID | 54241083 |
Filed Date | 2017-03-30 |
United States Patent
Application |
20170088718 |
Kind Code |
A1 |
Brown; Terry J. ; et
al. |
March 30, 2017 |
Conductive Paste With Improved Performance In Glass Strength
Abstract
Silver pastes including two powders having different physical
properties and silver flakes together with glass frits and pigments
impart improved thermal stress characteristics to substrates upon
firing.
Inventors: |
Brown; Terry J.;
(Pittsburgh, PA) ; Grover; Jeffery; (Bethel Park,
PA) ; Klimas; David; (Pittsburgh, PA) ;
Sakoske; George E.; (Independence, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ferro Corporation |
Mayfield Heights |
OH |
US |
|
|
Family ID: |
54241083 |
Appl. No.: |
15/126674 |
Filed: |
February 6, 2015 |
PCT Filed: |
February 6, 2015 |
PCT NO: |
PCT/US2015/014753 |
371 Date: |
September 16, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61974006 |
Apr 2, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C03C 2217/479 20130101;
C03C 2217/485 20130101; C03C 2217/48 20130101; C03C 8/18 20130101;
C03C 2217/70 20130101; C09D 5/24 20130101; H01B 1/16 20130101; C03C
3/066 20130101; H01L 31/022425 20130101; C03C 2204/00 20130101;
C03C 4/14 20130101; C03C 2205/00 20130101; C03C 8/04 20130101; C03C
17/04 20130101; C03C 3/089 20130101; C03C 8/16 20130101 |
International
Class: |
C09D 5/24 20060101
C09D005/24; C03C 8/18 20060101 C03C008/18; C03C 17/04 20060101
C03C017/04; C03C 3/089 20060101 C03C003/089; C03C 3/066 20060101
C03C003/066; C03C 4/14 20060101 C03C004/14; H01B 1/16 20060101
H01B001/16; C03C 8/04 20060101 C03C008/04 |
Claims
1. A lithium-free conductive paste comprising: a. 50-90 wt % of a
silver component, comprising i. 10-55 wt % of a first silver powder
having a tap density of 0.3-1.5 g/cc, ii. 10-35 wt % of a silver
flake having a tap density of 3.0-4.5 g/cc, and iii. 5-30 wt % of a
second silver powder having a tap density of 2.0-4.5 g/cc, b. 2-10
wt % of a glass component, comprising i. 25-50 wt %
Bi.sub.2O.sub.3, ii. 2-15 wt % ZnO, iii. 15-45 wt % SiO.sub.2, iv.
5-20 wt % B.sub.2O.sub.3, v. 1-10 wt % Na.sub.2O+K.sub.2O and vi.
0.1-10 wt % ZrO.sub.2 c. 0.1-5 wt % of a pigment selected from the
group consisting of i. CuCr.sub.2O.sub.4, ii.
(Co,Fe)(Fe,Cr).sub.2O.sub.4, and iii. (Fe,Co)Fe.sub.2O.sub.4, and
d. no lithium.
2. The conductive paste of claim 1, wherein the first silver powder
has a particle size D.sub.50 of 2-7 microns.
3. The conductive paste of claim 1, wherein the first silver powder
has a particle size D.sub.50 of 2.5-6.5 microns.
4. The conductive paste of claim 1, wherein the second silver
powder has a particle size D.sub.50 of 0.5-2.5 microns.
5. The conductive paste of claim 1, wherein the second silver
powder has a particle size D.sub.50 of 1-2 microns.
6. The conductive paste of claim 1, wherein the silver flake has a
particle size D.sub.50 of 1-4 microns.
7. The conductive paste of claim 1, wherein the silver flake has a
particle size D.sub.50 of 1.3-3.3 microns.
8. The conductive paste of claim 1, wherein the first silver powder
has a specific surface area of 0.5-1.5 m.sup.2/g.
9. The conductive paste of claim 1, wherein the second silver
powder has a specific surface area of 0.25-1.25 m.sup.2/g.
10. The conductive paste of claim 1, wherein the silver flake has a
specific surface area of 0.75-1.5 m.sup.2/g.
11. The conductive paste of claim 1, wherein the pigment further
comprises at least one selected from the group consisting of MnO,
Fe.sub.2O.sub.3, Al.sub.2O.sub.4, CuO, and NiO.
12. The conductive paste of claim 1, wherein the paste comprises:
a. 55-85 wt % of a silver component, comprising i. 15-50 wt %
silver powder having a tap density of 0.4-1.2 g/cc and a particle
size D.sub.50 of 2.5-6.5 microns, ii. 15-30 wt % of a silver flake
having a tap density of 3.2-4.2 g/cc and a particle size D.sub.50
of 1.3-3.3 microns, and iii. 10-28 wt % of a silver powder having a
tap density of 2.6-4.3 g/cc and a particle size D.sub.50 of 1-2
microns, b. 3-8 wt % of a glass component, comprising i. 25-50 wt %
Bi.sub.2O.sub.3, ii. 2-15 wt % ZnO, iii. 15-45 wt % SiO.sub.2, iv.
5-20 wt % B.sub.2O.sub.3, v. 1-10 wt % Na.sub.2O+K.sub.2O and vi.
0.1-10 wt % ZrO.sub.2 c. 1-2 wt % of a pigment selected from the
group consisting of i. CuCr.sub.2O.sub.4, ii.
(Co,Fe)(Fe,Cr).sub.2O.sub.4, and iii. (Fe,Co)Fe.sub.2O.sub.4, and
d. no lithium.
13. The conductive paste of claim 9, wherein the first silver
powder has a specific surface area of 0.6-1.3 m.sup.2/g.
14. The conductive paste of claim 9, wherein the second silver
powder has a specific surface area of 0.5-1 m.sup.2/g.
15. The conductive paste of claim 1, wherein the silver flake has a
specific surface area of 0.85-1.35 m.sup.2/g.
16. A substrate at least partially covered with a fired paste,
wherein the paste is the conductive paste of claim 1.
17. A method of reducing transient thermal stresses between a
coating and a substrate during firing, the method comprising: a.
applying to the substrate a lithium-free conductive paste, the
paste comprising: i. 50-90 wt % of a silver component, comprising:
1. 10-55 wt % of a first silver powder having a tap density of
0.3-1.5 g/cc, 2. 10-35 wt % of a silver flake having a tap density
of 3.0-4.5 g/cc, and 3. 5-30 wt % of a second silver powder having
a tap density of 2.0-4.5 g/cc, ii. 2-10 wt % of a glass component,
comprising: 1. 25-50 wt % Bi.sub.2O.sub.3, 2. 2-15 wt % ZnO, 3.
15-45 wt % SiO.sub.2, 4. 5-20 wt % B.sub.2O.sub.3, 5. 1-10 wt %
Na.sub.2O+K.sub.2O and 6. 0.1-10 wt % ZrO.sub.2 iii. 0.1-5 wt % of
a pigment selected from the group consisting of 1.
CuCr.sub.2O.sub.4, 2. (Co,Fe)(Fe,Cr).sub.2O.sub.4, and 3.
(Fe,Co)Fe.sub.2O.sub.4, and iv. no lithium, and b. firing the paste
at a firing temperature and time sufficient to sinter the silver
metal and fuse the glass component.
18. The method of claim 17 wherein the firing temperature is about
950.degree. F. to about 1400.degree. F.
19. The method of claim 17 wherein the firing temperature is about
1200.degree. F. to about 1300.degree. F.
20. The method of claim 17 wherein the firing time is about 1 to
about 300 seconds
Description
BACKGROUND OF THE INVENTION
1. Field of Invention
[0001] The invention relates to silver pastes demonstrating
comparable thermal coefficient properties relative to glass
substrates to which they are applied.
[0002] This invention relates to a conductive silver paste which,
when applied during the thermal fusing (firing) of the paste to a
glass, silicon, ceramic or ceramic glass enamel substrate, provides
conductivity and a thermal coefficient similar to the substrate,
thus reducing transient thermal stress differences from developing
between the coating and aforementioned substrates, that would
otherwise occur. The paste includes lower density silver powder,
high density silver powder, and medium density silver flake,
together with black pigment and a combination of lower expansion
glass frits, having different melting temperatures. The glass fits
are, and hence, the paste is, lithium free.
[0003] In particular, the present invention relates to a conductive
silver coating that includes a combination of lower expansion glass
frits having melting temperatures over a relatively wide range,
enabling the silver to produce less stress on the fired substrate
and increase over ties over an extended temperature range, thus
reducing thermal stress differences from developing between the
coating and the aforementioned substrates, that would otherwise
occur, especially if the firing cycle time is shortened.
2. Description of Related Art
[0004] Conventional conductive silver pastes are made with a low
melting fit which may contain oxides of lead, cadmium, lithium,
bismuth, zinc, boron and/or silica. The conductive pastes are
printed onto glass or ceramic substrates and fired to sinter and
bond the conductive paste to the substrate. Application of any type
of fired coating onto a glass substrate will weaken the glass
substrate.
BRIEF DESCRIPTION OF THE INVENTION
[0005] Accordingly, the art requires a conductive paste, which,
when applied and fired to a glass or ceramic substrate, does not
weaken the glass substrate, or at least weakens it to a lesser
extent than known conductive pastes. The invention overcomes the
drawbacks of the prior art as demonstrated hereinbelow.
[0006] An embodiment of the invention is a silver-containing paste
that imparts improved strength to a substrate upon which it is
applied and fired.
[0007] An embodiment of the invention is a silver-containing paste
that imparts improved strength to a substrate upon which it is
applied and fired.
[0008] An embodiment of the invention is a silver-containing paste
that reduces transient thermal stresses during firing, to a
substrate upon which it is applied and fired.
[0009] An embodiment of the invention is a conductive paste
including a silver component including first and second silver
pastes having different tap densities, and silver flakes. The paste
includes a glass component including at least one frit selected
from the group consisting of Bi.sub.2O.sub.3, ZnO, SiO.sub.2,
B.sub.2O.sub.3, Na.sub.2O, K.sub.2O and ZrO.sub.2. The paste may
also include an oxide pigment including oxygen and at least one of
copper, chrome, and iron.
[0010] An embodiment of the invention is a device including a
substrate to which a silver-containing paste is applied and fired,
wherein the presence of the paste during firing reduces transient
thermal stresses during firing, to the substrate upon which it is
applied and fired.
[0011] An embodiment of the invention is a conductive paste
comprising: (a) 50-90 wt % of a silver component, comprising (i)
10-55 wt % of a first silver powder having a tap density of 0.3-1.5
g/cc, (ii) 10-35 wt % of a silver flake having a tap density of
3.0-4.5 g/cc, and (iii) 5-30 wt % of a second silver powder having
a tap density of 2.0-4.5 g/cc, (b) 2-10 wt % of a glass component,
comprising (i) 25-50 wt % Bi.sub.2O.sub.3, (ii) 2-15 wt % ZnO,
(iii) 15-45 wt % SiO.sub.2, (iv) 5-20 wt % B.sub.2O.sub.3, (v) 1-10
wt % Na.sub.2O+K.sub.2O and (vi) 0.1-10 wt % ZrO.sub.2 (c) 0.1-2 wt
% of a pigment selected from the group consisting of (i)
CuCr.sub.2O.sub.4, (ii) (Co,Fe)(Fe,Cr).sub.2O.sub.4, and (iii)
(Fe,Co)Fe.sub.2O.sub.4. Alternate embodiments of the conductive
paste include the foregoing ingredients plus (d) 1-8 wt % of at
least one organic binder, and (e) 8-40 wt % of at least one organic
solvent. Alternate embodiments include conductive pastes including
any silver powders, flakes, glass components, pigments, organic
binders and organic solvents disclosed elsewhere herein in the
amounts elsewhere disclosed.
[0012] A further embodiment of the invention is a conductive paste
comprising: (a) 55-85 wt % of a silver component, comprising (i)
15-30 wt % silver powder having a tap density of 0.4-1.2 g/cc and a
particle size D.sub.50 of 2.5-6.5 microns, (ii) 15-30 wt % of a
silver flake having a tap density of 3.2-4.2 g/cc and a particle
size D.sub.50 of 1.3-3.3 microns, and (iii) 10-28 wt % of a silver
powder having a tap density of 2.6-4.3 g/cc and a particle size
D.sub.50 of 1-2 microns, (b) 3-8 wt % of a glass component,
comprising (i) 25-50 wt % Bi.sub.2O.sub.3, (ii) 2-15 wt % ZnO,
(iii) 15-45 wt % SiO.sub.2, (iv) 5-20 wt % B.sub.2O.sub.3, (v) 1-10
wt % Na.sub.2O+K.sub.2O and (vi) 0.1-10 wt % ZrO.sub.2, (c) 1-2 wt
% of a pigment selected from the group consisting of (i)
CuCr.sub.2O.sub.4, (ii) (Co,Fe)(Fe,Cr).sub.2O.sub.4, and (iii)
(Fe,Co)Fe.sub.2O.sub.4. Alternate embodiments include the foregoing
ingredients plus (d) 1-8 wt % of at least one organic binder, and
(e) 8-40 wt % of at least one organic solvent.
[0013] An embodiment of the invention is a substrate at least
partially covered with a fired paste, wherein the paste is any
conductive paste disclosed herein.
[0014] An embodiment of the invention is a method of reducing
transient thermal stresses comprising applying any conductive paste
disclosed herein to a substrate and firing the paste to sinter the
metals, i.e., silver, and fuse the glass component or glass frits
such that a conductive trace including silver metal and fused glass
is firmly affixed and integrated with the substrate.
[0015] An embodiment of the invention is a method of reducing
transient thermal stresses between a coating and a substrate during
firing, the method comprising: (a) applying to the substrate a
lithium-free conductive paste, the paste comprising: (i) 50-90 wt %
of a silver component, comprising: (1) 10-55 wt % of a first silver
powder having a tap density of 0.3-1.5 g/cc, (2) 10-35 wt % of a
silver flake having a tap density of 3.0-4.5 g/cc, and (3) 5-30 wt
% of a second silver powder having a tap density of 2.0-4.5 g/cc,
(ii) 2-10 wt % of a glass component, comprising: (1) 25-50 wt %
Bi.sub.2O.sub.3, (2) 2-15 wt % ZnO, (3) 15-45 wt % SiO.sub.2, (4)
5-20 wt % B.sub.2O.sub.3, (5) 1-10 wt % Na.sub.2O+K.sub.2O and (6)
0.1-10 wt % ZrO.sub.2 (iii) 0.1-5 wt % of a pigment selected from
the group consisting of (1) CuCr.sub.2O.sub.4, (2)
(Co,Fe)(Fe,Cr).sub.2O.sub.4, and (3) (Fe,Co)Fe.sub.2O.sub.4, and
(b) firing the paste at a firing temperature and time sufficient to
sinter the silver metal and fuse the glass component. Alternate
embodiments of the method of reducing transient thermal stress
include applying the paste including the aforementioned ingredients
plus (d) 1-8 wt % of at least one organic binder, and (e) 8-40 wt %
of at least one organic solvent. Further alternate embodiments
include the method involving conductive pastes including any silver
powders, flakes, glass components, pigments, organic binders and
organic solvents disclosed elsewhere herein in the amounts
elsewhere disclosed. Further alternate embodiments of the method
include firing at a firing temperature of about 950.degree. F. to
about 1400.degree. F., preferably about 1200.degree. F. to about
1300.degree. F., more preferably about 1200.degree. F. to about
1250.degree. F. Further alternate embodiments of the method include
firing at a firing time of about 1 to about 6000 seconds,
preferably about 1 to about 600 seconds, more preferably about 1 to
about 300 seconds, still more preferably about 1 to about 180
seconds, more preferably about 1 to about 150 seconds, still more
preferably about 60 to about 150 seconds.
[0016] The invention also includes an automotive glass, a solar
cell, and a home appliance including a coating comprising any paste
disclosed elsewhere herein, or including a coated substrate made at
least in part by any method disclosed elsewhere herein.
[0017] The foregoing and other features of the invention are
hereinafter more fully described and particularly pointed out in
the claims, the following description setting forth in detail
certain illustrative embodiments of the invention, these being
indicative, however, of but a few of the various ways in which the
principles of the invention may be employed.
DETAILED DESCRIPTION OF THE INVENTION
[0018] Based on the foregoing, the current art lacks a conductive
silver coating that can adequately fuse while minimizing the
thermal differences between the silver coating and the substrates
of interest (glass, silicon, ceramic, or ceramic enamel) during
short firing cycles and firing cycles requiring increased firing
temperatures, i.e., above about 1100.degree. F. The invention
permits conductive coatings to be made with a wider range of frits,
including those based on the borosilicates of zinc, bismuth, and
combinations thereof, and hence allows a wider firing range. The
silver coatings of the invention allow firing over wide temperature
ranges while ensuring good adhesion to the substrates, without
subjecting the assembly to increased thermal stresses. The fusion
temperature range of the glass fit and melting temperatures of
inorganic pigments and compounds set the upper limit of the firing
temperatures needed to adequately fuse the silver metal and other
inorganic materials together, and subsequently to the substrate,
without inducing further thermal stress.
[0019] Thermal stress is defined herein as the force per unit area
caused by the temperature difference over a small area. The
relevant area is an area of a substrate to which a paste or other
coating is applied and fired. The stress may be called "transient"
because it is short lived, that is, it is a factor only during
heating (i.e. firing) of a paste to secure adherence to a
substrate. to In particular, as the substrate and conductive silver
coating are heated, those portions of the substrate bearing a
conventional silver coating will have a lower temperature than
portions of the substrate not bearing such a coating. The
temperature difference creates thermal stress. The compositions of
the invention allow relatively consistent infrared absorption over
an extended firing temperature range, thus more closely matching
the thermal absorption of the coating to the thermal absorption
rate of the substrate, such as a high-IR absorbing black ceramic
enamel, resulting in closer thermal equilibrium between the
conductive silver coating and the substrate. Hence, thermal stress
during the formation of such conductive coatings on substrates such
as glass, enamel, ceramic, and ceramic-enamel is reduced.
[0020] The conductive silver pastes of the invention permit firing
temperatures of about 950.degree. F. up to about 1400.degree. F.,
preferably about 1200.degree. F. to about 1300.degree. F., more
preferably about 1200.degree. F. to about 1250.degree. F. An
alternate preferred firing range is about 1300.degree. F. to about
1400.degree. F. It is believed that the combination of silver
powders distinct morphologies and particle size distributions and
silver flakes together with glass frits based on Bi.sub.2O.sub.3,
ZnO, SiO.sub.2, B.sub.2O.sub.3, Na.sub.2O, K.sub.2O and ZrO.sub.2
provide uniquely matched thermal expansion coefficients suitable
for use with a variety of metal, glass, ceramic, and enamel
substrates.
[0021] Pigments such as CuCr.sub.2O.sub.4,
(Co,Fe)(Fe,Cr).sub.2O.sub.4, and (Fe,Co)Fe.sub.2O.sub.4, as well as
optional oxide-modifiers such as MnO, Fe.sub.2O.sub.3,
Al.sub.2O.sub.4, CuO, and NiO are used to maintain a high level of
infrared absorption up to about 1400.degree. F. This permits
increased firing temperatures, and hence speeds (i.e., decreases)
firing cycle times, without inducing additional thermal stress.
Firing times envisioned by the invention at temperatures disclosed
elsewhere herein are about 1 to about 6000 seconds, preferably
about 1 to about 600 seconds, more preferably about 1 to about 300
seconds, still more preferably about 1 to about 180 seconds, more
preferably about 1 to about 150 seconds, still more preferably
about 60 to about 150 seconds.
[0022] The conductive pastes of the invention include several major
components: silver powders, silver flakes, glass frits, pigments,
pigment modifiers, organic binders and solvents. Each is detailed
in turn hereinbelow.
[0023] Silver Powders and Flakes. The silver powders useful herein
have a generally spherical shape. Broadly, the powders and flakes
possess the properties listed in the following table. It is
understood that a given powder or flake may possess any or all of
the properties in a given row. Each different combination of
properties for a given powder or flake constitutes a separate
powder or flake that can be used and claimed in the invention.
Combinations of properties for a given powder or flake from this
table and others herein may be considered separate powders or
flakes. Broadly, the pastes of the invention include 50-90 wt % of
silver in any form. In a preferred embodiment, the pastes of the
invention include 50-85 wt % silver in any faun. In a more
preferred embodiment, the pastes include 50-83 wt %, and in a more
preferred embodiment, the pastes include 55-80 wt % of silver in
any form. Totals of subranges of different silver constituents (two
powders and the flake) are understood to add up to the overall
silver range even if the sum of the constituent ranges could fall
under or exceed such overall silver range. Similarly, an overall
composition is presumed to contain 100 wt % of total
ingredients.
TABLE-US-00001 TABLE 1 Silver powders and flakes useful in the
invention. Tap Fisher Surface Density Sub Sieve Area PSD 95% PSD
90% PSD 50% PSD 10% Specs (g/ml) (.mu.m) (m.sup.2/g) (.mu.m)
(.mu.m) (.mu.m) (.mu.m) Wt % Powder 1 0.3-1.5 0.7-2.4 0.3-1.5
<40 <30 2-7 0.9-3.4 10-55 Flake 3.0-4.5 -- 0.75-1.5 -- <20
1-4 0.5-1.3 10-35 Powder 2 2.0-4.5 0.7-1.5 0.4-1.2 <10 <7
0.5-2.5 0.3-1.3 5-30
TABLE-US-00002 TABLE 2 Preferred powder and flake properties. Tap
Fisher Surface Density Sub Sieve Area PSD 95% PSD 90% PSD 50% PSD
10% Specs (g/ml) (.mu.m) (m.sup.2/g) (.mu.m) (.mu.m) (.mu.m)
(.mu.m) Wt % Powder 1 0.4-1.2 0.85-2.1 0.6-1.3 <30 <20
2.5-6.5 .sup. 0.75-3.25 10-55 Flake 3.2-4.2 -- 0.85-1.35 -- <13
1.3-3.0 0.6-1 10-35 Powder 2 2.6-4.3 0.8-1.35 0.5-1.sup. <7
<5 1-2 0.5-1 5-30
[0024] A wide variety of Silver Powders and Silver Flakes are
commercially available from Ferro Corporation, Cleveland, Ohio. and
sold under product names SPC, SFW and SFC20ED. Powder SPC20ED falls
within "Powder 1" in the tables above; Powder SPC falls within
"Powder 2" above, and SFW falls within "Flake" above. The
abbreviation PSDxx means particle size Dxx, where xx can be 10, 50,
90 or 95. Particle size D.sub.95 means that 95% of all particles in
a sample are smaller than the listed value, in microns, similarly
for D.sub.90. Particle size D.sub.50 is the value in microns at
which 50% of the particles are larger and 50% are smaller. Particle
size D.sub.10 is a value in microns at which 10% of particles are
smaller.
[0025] Ferro Corporation also sells other appropriate silver metal
powders and silver metal flakes. Tap Density is a measure of the
volume that a given weight of material will occupy after undergoing
a certain amount of prescribed compaction as known in the art;
reported as g/cc. Surface Area is determined by at least one of two
techniques: permeametry by a Fisher Sub Sieve Sizer (FSSS); and gas
absorption (Brunauer-Emmett-Teller method (BET)) by
Quantachrome.
[0026] Glass Component. The pastes of the invention contain 1-10 wt
% of a glass component, preferably 2-10 wt %, more preferably 4-10
wt % and still more preferably 5-9 wt %. The glass component may
contain one or more glass frits. The glass fits useful herein are
not particularly limited. However, preferred frits include oxides
of at least one of zinc, and bismuth; combinations of the foregoing
are also suitable. Further frit compositions may be found in Table
3. The frits useful in the invention have a CTE of
50-90.times.10-7, preferably 55-85.times.10-7 and more preferably
60-83.times.10-7, and are considered lower expansion frits. This is
in contrast to prior art higher expansion fits which have CTEs in
the range of 100-150.times.10-7.
TABLE-US-00003 TABLE 3 Glass frit compositional ranges. Glass
Composition Ingredient (wt %) I II III Bi.sub.2O.sub.3 22-51 27-48
30-45 ZnO 2-20 3-18 5-15 SiO.sub.2 15-50 18-45 20-40 B.sub.2O.sub.3
5-25 8-22 10-15 Na.sub.2O + K.sub.2O 3-20 4-15 5-9 F 0.1-8 0.5-5
1-3 ZrO.sub.2 0.25-10 0.5-8 1-5 TiO.sub.2 0-7 0-5 0.1-2 Li, Pb, Cd
in any form 0 0 0
[0027] Glass fits for various embodiments may be constructed using
ranges from different columns of Table 3 or other tables. Also, for
any range bounded by zero, the table is to be read as alternately
disclosing the same range bounded at the lower end by 0.01 or
0.1.
[0028] Black Pigment. The compositions of the invention further
include one or more inorganic black pigments (separate from carbon
black, noted above). Suitable pigments herein include
CuCr.sub.2O.sub.4 and (Co,Fe)(Fe,Cr).sub.2O.sub.4 and the like.
Examples include pigments available from Ferro Corporation,
Washington Pa., such as 2991 pigment (copper chromite black), 2980
pigment (cobalt chromium iron black), 2987 pigment (nickel
manganese iron chromium black), and 0-1776 pigment (copper chromate
black). In the presently most preferred embodiment of the
invention, the inorganic black pigment is copper chromite spinel,
available from Ferro Corporation as V-7702 or V-7709. The black
pigments may be used in the paste formulation in an amount of 0.1-5
wt %, preferably 0.2-4 wt %, more preferably 0.5-3 wt % and more
preferably 1-2 wt %.
[0029] Pigment Modifiers. Various oxides have been identified as
useful to modify or extend the properties of the pigments disclosed
hereinabove. The pastes or pigments of the invention may further
include any of MnO, Fe.sub.2O.sub.3, Al.sub.2O.sub.4, CuO, and
NiO.
[0030] Organic Medium. The organic medium comprises a binder and a
solvent, which are selected based on the intended application. It
is essential that the medium adequately suspend the particulates
(i.e., metal powders, glass frit, pigment, etc.) and burn off
completely upon firing. Broadly, the organic medium may include
petroleum/pine oil based solvents, ester alcohol based solvents,
tridecyl alcohol based solvents, thermoplastic wax based binders,
and/or water miscible glycol based solvents. Simple aqueous
solvents also may be used.
[0031] In particular, binders including methyl cellulose, ethyl
cellulose, and hydroxypropyl cellulose, polystyrene, modified
polystyrene, and combinations thereof, may be used. Suitable
solvents include glycols such as ethylene glycol, propylene glycol
and hexylene glycol; higher boiling alcohols such as Dowanor
(diethylene glycol monoethyl ether); butyl Carbitol.RTM.
(diethylene glycol monobutyl ether); dibutyl Carbitol.RTM.
(diethylene glycol dibutyl ether); butyl Carbitol.RTM. acetate
(diethylene glycol monobutyl ether acetate); Texanol.RTM.
(2,2,4-trimethyl-1,3-pentanediol monoisobutyrate), as well as other
alcohol esters, kerosene, and dibutyl phthalate, diethylene glycol
butyl ether; alpha-terpineol; beta-terpineol; gamma terpineol;
tridecyl alcohol (trade name Exxal 13, for example); diethylene
glycol ethyl ether (Carbitol.TM.), diethylene glycol butyl ether
(Butyl Carbitol.TM.); pine oils, vegetable oils, mineral oils, low
molecular weight petroleum fractions, tridecyl alcohols, and
synthetic or natural resins and blends thereof. Products sold under
the Texanol.RTM. trademark are available from Eastman Chemical
Company, Kingsport, Tenn.; those sold under the Dowanol.RTM. and
Carbitol.RTM. trademarks are available from Dow Chemical Co.,
Midland, Mich. Surfactants and/or other film forming modifiers can
also be included.
[0032] Mediums including having Ferro Corporation product numbers
of 1331, 1456, 1562 and 1652 and C92 may also be used. Mediums 1331
and 1356 include ethyl cellulose and tridecyl alcohol in differing
amounts. Medium C92 is a combination of ethyl methacrylate,
Texanol.RTM., Exaal.RTM. 13 and Diethylene Glycol Monobutyl Ether
Acetate.
TABLE-US-00004 TABLE 4 Formulas of Mediums useful in the Invention.
Wt % Ingredient/Purpose Medium 1356 80-90 Tridecyl alcohol 7-13
Binder resin 1-7 Methyl ester of hydrogenated rosin 0.1-4
Dispersant Medium 1562 70-83 Terpineol alcohol 4-9 Ester alcohol
9-17 Acrylic resin 0.01-1 Sodium dioctyl sulfosuccinate 0.5-3
Dispersant Medium C92 29-41 2,2,4 Trimethyl-1,3 Pentanediol
Monoisobutyrate 19-29 Tridecyl alcohol 14-25 Acetate of Glycol
ether DB or Acetate of butyl Carbitol 10-19 Acrylic resin
binder/film former 4.5-9.7 wetting and dispersing agent Medium 1652
47-72 Terpineol alcohol derived from pine oil 28-53 Polyterpene
resin
[0033] Dispersing Surfactant. A dispersing surfactant assists in
pigment wetting, when an insoluble particulate inorganic pigment is
used. A dispersing surfactant typically contains a block copolymer
with pigment affinic groups. For example, surfactants sold under
the Disperbyk.RTM. and Byk.RTM. trademarks by Byk Chemie of Wesel,
Germany, such as Disperbyk 110, 140, and 163, which are solutions
of high molecular weight block copolymers with pigment affinic
groups, and a blend of solvents. Disperbyk 110 is a 1:1 blend of
methoxypropylacetate and alkylbenzenes. Disperbyk 140 is a solution
of alkyl-ammonium salt of an acidic polymer in a
methoxypropylacetate solvent. Disperbyk 163 has the solvents
xylene, butylacetate and methoxypropylacetate in a 4/2/5 ratio.
[0034] Rheological Modifier. A rheological modifier is used to
adjust the viscosity of the green pigment package composition. A
variety of rheological modifiers may be used, including those sold
under the Byk.RTM., Disperplast.RTM., and Viscobyk.RTM. trademarks,
available from Byk Chemie. They include, for example, the BYK 400
series, such as BYK 411 and BYK 420, (modified urea solutions); the
BYK W-900 series, (pigment wetting and dispersing additives); the
Disperplast series, (pigment wetting and dispersing additives for
plastisols and organosols); and the Viscobyk series, (viscosity
depressants for plastisols and organosols).
[0035] Examples. As set forth in Table 5, silver pastes were
prepared using Ferro Corporation silver powders SPC 20ED, and SPC,
and silver flakes SFW, which correspond to Powders 1 and 2 and
Flake, respectively, in Tables 1 and 2. The pastes also include
Glass Frits A, B C, and D, organic vehicles C-92 and 1356, P95-1W
is a Cu--Cr black pigment containing a minor amount of Mn,
available from Asahi Sangyo Kaisha Ltd., Tokyo, Japan, and in some
cases TDA (tridecyl alcohol), Texanol.RTM., and/or Disperbyk.RTM.
111. Frits A, B, C and D are characterized in Tables 7-10, while
frit formulation advice and frit properties are given in Table
11.
TABLE-US-00005 TABLE 5 Exemplary paste compositions and viscosity
data. Wt % CCL-460-B CCL-265-B CCL-228 CCL-268-B CCL-275 CCL-380-B
Overall Silver content 60 69.5 68 72 75 80 SPC20ED 14.17 17.5 45.09
17 51.04 25 SFW 20.83 23.7 13.05 25 13.03 30 SPC 25 28.3 30 25
SP-335 Ag powder 11.02 SFQED 10 Nickel SP-10 7 2.98 CCL-029 0.5 0.5
Frit A 1.67 1.75 2 0.25 Frit B 1.67 3.25 2 3.5 Frit C 2.5 2.5 3.5 2
Frit D 8 7.97 P95-1W 1.4 1.5 1.5 1.25 C 92 16.09 14.15 11 8.38 9
1331 13 1356 16.57 7.1 0.18 6 3.49 1.75 TDA 0.1 2 Texanol 0.25 0.79
1.25 Brij 93 0.5 Disperbyk111 0.5 0.79 1 Exaal 13 2.18 Totals 100
100 100 100 100 100 Viscosity Data (70.degree. F.) 7 spindle cps
cps n.m. cps n.m. cps 0.5 rpm 200000 376000 384000 632000 10 74000
72400 68800 67200 20 61600 55200 51000 44600 50 49600 39920 36000
29440 100 41600 29240 28500 27400
[0036] SP-335 is a silver powder having tap density 2.7 to 3.6,
apparent density 23.2 to 32 grams/cubic inch, and surface area 0.75
to 1.4 m.sup.2/gram.
[0037] Yelkin.RTM. is a surface active lecithin product from Archer
Daniels Midland Co, Decatur, Ill. Also, shear rate can be
calculated from spindle RPMs by the equation RPM.times.spindle
factor=shear rate. The spindle factor for the #7 spindle is 0.209.
"N.M." means not measured.
TABLE-US-00006 TABLE 6 Successive trials based on CCL-268-B. Wt %
CCL-268 3B 4B 5B 6B 7B SPC20ED 45 17 17 15 15 17 SFW flake 13 25 25
27 27 25 SPC 30 30 30 30 30 335 Ag powder 10 Nickel SP-10 7 CCL-029
0.5 Frit A 2 2 2 4 Frit B 2 2.5 2 Frit C 3.5 3.25 4 2 3.5 Frit D
(E-8044) 8 FS2871 5.5 P95-1W 1.5 2 3.5 1.5 Ultrox 1.0 C-92 13.1
1652 4 4 3.15 2.15 4 1356 3.4 6 6 5.5 5.5 6 TDA 8.5 9.25 9.25 9.25
8.5 extra TDA 0.12 0.12 Yelkin 0.05 0.1 0.1 0.05
[0038] In the table above, Ultrox.RTM. is a zirconium silicate
commercially available from Trebol USA, Andrews, S.C.
[0039] Tables 7-9. Exemplary Frit compositions. The fits useful
herein are free of lithium and have the following compositional
ranges. Tables 7-9 each represent one frit (Frits A, B and C), with
the columns representing broad, preferred and more preferred ranges
for each fit. Frit A corresponds to commercially available Ferro
product E-8008, while Frits B and C correspond, respectively, to
Ferro Corporation products E-8018 and E-8027. Frit D corresponds to
Ferro Corporation frit E-8044. E-8018 may be termed a low expansion
frit, while E-8027 is an ultra low expansion frit.
TABLE-US-00007 TABLE 7 Exemplary formulation ranges for Frit A.
More Oxides Broad Preferred Preferred Bi2O3 37-51 38.5-49.2
41.1-47.8 ZnO 11-21 12.2-19.8 13.4-18.7 SiO2 12-25 14.3-23.2
16.9-21.7 B2O2 7.2-16.7 8.4-14.8 9.1-13.2 Na2O 1.7-7.7 2.5-6.1
3.1-5.9 F 0.9-3.4 1.3-3.1 1.7-2.8 ZrO2 0.7-2.1 0.9-1.8 1.1-1.7 TiO2
0.8-2.4 1.1-2.2 1.3-1.8 totals 100 100 100
TABLE-US-00008 TABLE 8 Exemplary formulation ranges for Frit B.
More Oxides Broad Preferred Preferred Bi2O3 37.2-51.1 39.3-47.8
41.4-46-6 ZnO 1.7-5.1 2.2-4.8 2.5-4.3 SiO2 28.7-33.6 29.3-32.8
29.9-31.7 B2O2 11.9-17.2 12.7-16.8 13.2-15.7 Na2O 4.7-9.1 5.2-8.2
5.9-7.5 F 0 0 0 ZrO2 0.7-2.4 0.9-2.1 1.1-1.8 TiO2 0 0 0 totals 100
100 100
TABLE-US-00009 TABLE 9 Exemplary formulation ranges for Frit C.
More Oxides Broad Preferred Preferred Bi.sub.2O.sub.3 26.2-33.1
27.5-32.2 28.2-30.9 ZnO 2.1-8.8 3.0-6.9 3.4-5.8 SiO.sub.2 38.5-43.2
39.2-42.2 39.7-41.8 B.sub.2O.sub.3 11.2-15.7 12.3-15.1 13.1-14.4
Na.sub.2O 3.9-8.7 4.4-7.9 5.1-7.4 F 0 0 0 ZrO2 2.7-8.1 3.2-7.1
3.9-6.4 TiO2 0 0 0 totals 100 100 100
TABLE-US-00010 TABLE 10 Exemplary formulation ranges for Frit D.
More Oxides Broad Preferred Preferred Bi2O3 48.2-56.9 49.1-55.3
50.4-54.1 ZnO 5.9-10.2 6.8-9.7 7.4-9.1 SiO2 21.6-30.3 23.2-28.5
24.4-27.2 B.sub.2O.sub.3 5.8-11.3 6.4-10.2 6.9-9.4 Li.sub.2O
0.7-4.4 1.2-3.9 1.6-2.8 Na2O 1.1-4.9 1.6-4.1 2.2-3.4 K.sub.2O
0.4-2.8 0.6-2.2 0.8-1.7 F 0.1-2.2 0.2-1.7 0.3-1.1 ZrO2 0.1-2.7
0.2-2.1 0.3-1.4 TiO2 0.3-3.1 0.5-2.4 0.6-1.7 totals 100 100 100
TABLE-US-00011 TABLE 11 Properties of Frits A-D from formulations
in Table 4. Frits % range CTE of frit minimum fire Frit A 0.25-2.5%
80 .times. 10-7 1110.degree. F. Frit B 1.5-3.5% 83 .times. 10-7
1090 Frit C 2.0-3.75% 65 .times. 10-7 1170 Frit D Not measured 87
.times. 10-7 Not measured
[0040] In the above table, minimum fire is the lowest temperature
where the frit will fuse and form a non-porous coating.
TABLE-US-00012 TABLE 12 Summary of Percentage Strength Reduction of
PPG and Guardian glass plates when printed and fired with Inventive
Frits. *Averaged Percentage *Percentage Strength Strength Reduction
Based on Reduction Based on Firing Averaged Total Averaged Tension
Temperature Calculated Stress to Stress from the (.degree. F.)
Cause Failure (psi) Mirror Radius (psi) Group Screen Printed Air
Surface Tin Surface Air Surface Tin Surface Control 1220 68 69 69
71.5 Control 1235 70 NA 75 NA w/o Nickel 1220 NA 65 NA 71.5
w/Lithium w/o 1220 NA 60 NA 66 Nickel, with Frit B
[0041] In Table 12, Control is a state of the art paste that
contains lithium and does not contain low expansion frits.
[0042] In Table 13 that follows, several examples of inventive and
prior art pastes are applied to commercially available glass plates
(from PPG or Guardian) and fired at a temperature at a time
indicated.
TABLE-US-00013 TABLE 13 Properties of Silver pastes fired on Glass
plates. Firing Averaged *Averaged Percentage Glass Glass
Temperature Tension Stress Strength Reduction Based on Plate
CCL-268 Group ID, Enamel, or (.degree. F.) from Mirror Averaged
Tension Stress Supplier Combo Time (Minutes) Radius (Psi) from
Mirror Radius (Psi) PPG Control N/A 24,390 N/A PPG JMatthey 2T1730
(no Ag) 1226/1:50 11,250 54 PPG CCL-268 1221/2:00 3,962 84 PPG
CCL-268 overprinted with JM 1222/2:28 2,470 89 2T1730 PPG CCL-268
no Nickel; w/ E-8018 1221/1:55 3,980 84 PPG CCL-268-3B no nickel
1221/2:23 7,620 69 with black pigment Low "E" silver and E-8027 PPG
CCL-268-4B no Ni 1231/2:31 4,900 80 with additive to lower
expansion and E-8027 PPG CCL-268-5B no nickel with E- 1221/2:21
5,900 76 8018 with black pigment) PPG CCL-268-6B no nickel with E-
1221/2:21 5,900 76 8018 and black pigment Guardian Control N/A
21,970 N/A Guardian JMatthey 2T1730 1226/1:50 11,030 50 Guardian
CCL-268 1221/2:00 3,046 86 Guardian Ferro CCL-268 + silver
1222/2:28 2,400 89 overprinted with Johnson Matthey 2T1730 Guardian
CCL-268 no Nickel/ 1221/1:55 4,710 79 with E-8018 Guardian
CCL-268-3B no nickel 1221/2:23 6,640 70 with black pigment Low "E"
silver and E-8027 Guardian CCL-268-4B no nickel 1231/2:31 5,220 76
with additive to lower expansion and E-8027 Guardian CCL-268-5B no
nickel 1221/2:07 5,270 76 E-8018 and black pigment Guardian
CCL-268-6B no nickel 1221/2:07 4,870 78 with E-8018 and black
pigment Guardian Clear Inboard Ply "Control" Exit Temp 23,370 N/A
Samples removed from 1220-1225.degree. C. sections above bottom
grid/ enamel band area. Guardian Samples removed bottom Exit Temp
5,640 76 sections of Ag grid/enamel 1220-1225.degree. C. band area
(Ferro CCL-268 silver overprinted with JMatthey 2T1730 enamel)
[0043] Low expansion frit is E8018, and extra low expansion frit is
E-8027.
[0044] In the table above, Control means that the glass print is
fired with no silver and no black enamel. JM 2T1730 is Johnson
Matthey black enamel and the corresponding sample is a test with
the black enamel only and no silver printed on glass.
[0045] CCL-268 (68% Ag) sampled from a production lot retain showed
averaged 72% percent of glass strength (similar to CCL-228).
CCL-268B (72% Ag) lab sample averaged 49% percent glass strength
decrease with an averaged basic strength of 4010 psi tension that
exceeded the glass/silver basic strength range of 1880 to 2820 psi
tension. Ferro CCL-268B (nickel-free) silver paste sampled from
production lots exhibited identical glass strength reduction of
60%. The average basic strength values for these two groups
averaged 3032 psi tension that exceeded the glass/silver basic
strength range of 1880 to 2820 psi tension.
[0046] CCL-380 (80% Ag) sampled from a production lot retain
averaged 77% percent glass strength decrease. CCL-380B (80% Ag lab
sample dated 6-20-2013 averaged 68% percent glass strength decrease
with a basic strength of 2413 psi tension that is within the
glass/silver basic strength range of 1880 to 2820 psi tension.
[0047] Both the Ferro CCL-380B (nickel free) lab sample and the
CCL-380 nickel version silver paste averaged approximate strength
reductions of 76%. The lab sample exhibited a basic strength of
1793 which is below the glass/silver basic strength range of 1880
to 2820 psi tension.
TABLE-US-00014 TABLE 14 Ferro Silver pastes with or without Nickel,
Fired on PPG or Guardian Glass Plates. Averaged Percentage Silver
Paste Averaged Glass Strength Glass Glass Group ID, Firing Temp
Glass Tension Stress Reduction Based on Plate Glass Thickness Paste
Enamel, or (.degree. F.)/Time Surface from Mirror Averaged Tension
Stress Supplier Type (mm) Supplier Combo Silver % (Min) Tested
Radius (Psi) from Mirror Radius (Psi) PPG/PGW Clear 1.6 Ferro
CCL-268 68 1221/2:00 Air 3,962 84 PPG/PGW Clear 1.6 Ferro
CCL-268-3B 72 1221/2:23 Air 7,620 69 Guardian Clear 1.6 Ferro
CCL-268 68 1221/2:00 Air 3,046 86 Guardian Clear 1.6 Ferro
CCL-268-3B 72 1221/2:23 Air 6,640 70 PPG/PGW Solex 2.1 Ferro
CCL-268 68 1220/3:25 Tin 5,110 72 PPG/PGW Solex 2.1 Ferro
CCL-268-3B 72 1221 ~3:00 Tin 9,340 49 PPG/PGW Solex 2.1 Ferro
CCL-228 w/Ni 68 1221 ~3:00 Tin 5,370 70.5 PPG/PGW Solex 2.1 Ferro
CCL-228B no Ni TBD 1220 in 3:07 Tin 5,900 68 PPG/PGW Solex 2.1 mm
Ferro CCL-275 w/Ni 75 1,220 in 3:00 Tin 4,390 76 PPG/PGW Solex 2.1
mm Ferro CCL-275B no Ni 76 1,220/3:25 Tin 4,400 76 with E-8027
PPG/PGW Solex 2.1 mm Ferro CCL-380 w/Ni 80 1,220/3:25 Tin 4,159
77
[0048] In the table above, "air" means that the silver was printed
on the air surface of the molten float glass, while "tin" means the
silver was printed on the tin surface of the glass.
[0049] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
illustrative example shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general invention concept as defined by the
appended claims and their equivalents.
* * * * *